Added:
- proper substitutions in BinExpr
- Possibly naïve version of constraint solving (works for example in slides)

Removed:
- type Tms = [Tm]
- special cases of show instance for TySchemes (seems to be incorrect)
Easier definition of possibly incomplete constraint solving (subst was already applied)
Showing all interesting types (after complete substitution), with their annotation variables.
Followed by what values these annotation variables actually have, as constraint solving taught us.
Added undefineds to the semantics of LCons / LNil synthesized attribute res